There is nothing to prevent you from distributing a single .deb file which includes unmolested Linux kernel source code, unmolested ZFS source code, and any patches required; and then, during the post-installation script, actually compiles the kernel and ZFS together before installing the resulting binaries. The licence agreements themselves say you can distribute source code; and the Law of the Land says that if you acquired it legitimately, then you must be allowed to compile and run it, otherwise it would not be fit for purpose.
However, you can't redistribute the resulting binary without exceeding the permissions granted by one or the other licence. Which creates an interesting paradox. If two possible chains of events have the same ultimate consequence, can one be right and the other wrong?
Given two .deb archives; one of which automatically patches and compiles the Source Code, installs the new kernel then removes the original Source Code, and the other of which simply installs identical binaries that may not legally be distributed, and without paying attention to the time taken for the installation process to complete nor the amount of disk space occupied in the meantime, there would be no discernible difference in the state of a file system after either one had been installed.
I suppose there is a physical-world parallel with articles that might be legal to make for oneself, but not to pass to anyone else and especially not if money is changing hands. But a self-compiling .deb archive is like a kit of parts, each innoucuous in its own right, all spring-loaded to assemble themselves into position the instant they are shaken out of the box .....
This one could run and run.